Sunday, 3 May 2020

'Arms race' between bacteria and viruses

University
of Otago researchers have contributed to an international study which helps
improve the understanding of bacteria and viruses.

The
study reveals how bacterial immune systems can be harmful for their hosts, and
why they are not found in all bacteria.

Researchers
at the University of Exeter in the UK, with support from the University of
Montpellier in France and the Otago team, made the surprising finding that
existing CRISPR anti-viral immunity was often a disadvantage to the bacterium
when infected by certain viruses.

CRISPR has become
well known for its repurposing as a tool for precise genetic
engineering. However, CRISPR systems (segments of DNA) naturally occur in many
bacteria and have the important function of providing bacteria with immunity
against viruses or foreign DNA.

This
triggered a major question as to whether autominnunity is important in other
bacterial pathogens. Otago researchers Dr Chris Brown, Dr Teyuan Chyou and
Professor Peter Fineran, used bioinformatics to address this question by
analysing more than 170,000 bacterial genomes, including diverse pathogens. The
software used was developed by the Brown and Fineran groups at the University
of Otago, while recent Otago PhD graduate Bridget Watson contributed to the
experiments in the UK.

"We
searched the DNA sequence for CRISPR systems and integrated viral genomes. We
found that CRISPR autoimmunity was likely to be widespread in nature," Dr
Brown says.

Professor
Fineran explains this suggested that triggering the powerful CRISPR defence
systems is risky for a bacterium. "Importantly, this may help answer a
long-standing question of why these defence systems are absent in 60 per cent
of bacteria."

For
example, Staphylococcus aureus pathogens that often take up extra genes to
become multidrug resistant, seldom have CRISPR defence. An example of this is
MRSA (Methicillin-resistant Staphylococcus aureus) an infection often occurring
in people who have been in hospitals or other healthcare settings like
residential care homes, which has become resistant to many of the antibiotics
used to treat ordinary staph infections. It seldom has CRISPR defence.

This
study forms part of larger studies aimed at understanding the arms race between
bacteria and their viruses and has significant implications.

"Importantly,
this change in understanding of pathogen defence systems will inform the design
of new treatments, particularly those using viruses that kill pathogenic or
antibiotic resistant bacteria," Dr Brown explains.